1. Field of the Invention
This invention relates generally to a quench strobe having a predetermined quench rate and, more particularly, to a quench strobe wherein the quench rate is predetermined to increase the exposure at the film plane by an amount substantially approximating the additional exposure normally incurred during the shutter blade closing time when the scene is illuminated under generally steady state lighting conditions.
2. Description of the Prior Art
Electronic photograhic strobe devices of the type in which the flashlight produced by the flash tube of the device is automatically terminated after a predetermined quantity of light has been received from the scene being photographed by a light-responsive control portion of the device are well known in the art. Such strobes are commonly referred to as quench strobes. In addition to having an independent light-responsive control circuit in the strobe, it is also well known to utilize the exposure control circuit associated with the actual camera apparatus to control the firing and quenching of a strobe unit as is more fully disclosed in U.S. Pat. No. 3,776,112, by Wilwerding issued 1973. Wilwerding discloses a circuit coupled to the light-integrating exposure control circuit of a camera to effect the flash quenching of an electronic flash unit. Thus, it is well known to couple an electronically controlled shutter camera with a quenchable electronic strobe unit so that the strobe unit is quenched simultaneously with the command signal to return the shutter blade elements to their closed position.
Such an arrangement, however, would not be compatible with an exposure control system of the type described in a copending application for U.S. application Ser. No. 619,384 entitled "Exposure Control System With Fill-Flash Race Condition" by Edwin K. Shenk, filed Sept. 30, 1975. The aforementioned exposure control system is utilized in conjunction with a shutter blade arrangement of the so-called "scanning type" which embodies a pair of shutter blade elements, each of which includes a primary aperture therethrough to cooperatively define a gradually varying effective aperture size as a function of the position of the shutter blade elements. Each shutter blade element additionally includes a photocell sweep secondary aperture which apertures also cooperatively define a gradually varying effective secondary aperture in front of the exposure control photocell as a function of blade position. The photocell sweep secondary apertures are generally configured to progressively open ahead of the primary aperture so that the exposure control circuit effects the closing of the shutter blade elements at a time prior to which the film is fully exposed. Prematurely signalling the shutter blade elements to close prior to the time required for a full film exposure anticipates for the additional scene light which will impinge upon the film during the finite time required for the shutter blade elements to fully close. Thus, quenching the strobe solely as a function of the exposure control system command signal to initiate closing of the shutter blade elements as disclosed in U.S. Pat. No. 3,776,112, supra will result in an under-exposure since the strobe is quenched almost instantaneously.
In response to this problem, it has been recently proposed to utilize an additional time delay circuit in conjunction with a quench strobe so that the strobe is quenched subsequent to the expiration of a predetermined time delay subsequent to command signal to close the shutter blade elements of the camera. In this manner, additional illumination is provided to influence the exposure during the shutter blade closing time as would otherwise be provided if the scene were illuminated by normal ambient light or an ordinary flash bulb. Thus, a quench strobe may be used interchangeably with an ordinary flash bulb and the shutter blade closing command signal may be utilized to initiate the time delay after which the strobe is quenched. Various arrangements for such time delay quench strobes are further discussed in United States Applications Ser. No. 684,902 entitled "Time Delay Quench Strobe With Improved Fill-In Flash Performance" filed May 10, 1976 in common assignment herewith, Ser. No. 686,020 entitled "Scene Light Responsive Variable Quench Time Delay For Quench Strobe" filed May 13, 1976 in common assignment herewith, Ser. No. 674,937 entitled "Fixed Time Delay Circuit for Quench Strobe" filed Apr. 8, 1976 in common assignment herewith and Ser. No. 674,840 entitled "Fixed Time Delay Quench Strobe" filed Apr. 8, 1976 in common assignment herewith. Such time delay circuits, although entirely satisfactory in performance, provide an additional circuit complexity to the strobe which would better be eliminated in the interests of economy and simplicity.
Therefore it is a primary object of this invention to provide a quench strobe which may be quenched at a predetermined rate which controls the amount of artificial illumination emitted subsequent to the initial command signal to quench.
It is also an object of this invention to provide a quench strobe with a predetermined quench rate which provides for substantially the same amount of exposure influencing artificial illumination subsequent to the shutter blade closing command signal as would otherwise be provided by a normal generally steady state illuminated scene.
It is a further object of this invention to provide a quench strobe with a predetermined quench rate which tailors the amount of exposure influencing artificial illumination emitted during the time required for the shutter blade elements to return to their closed position to correlate with the amount of extra exposure which is automatically anticipated by the exposure control system of the camera.
Other objects of the invention will in part be obvious and will in part appear hereinafter. The invention accordingly comprises the mechanism and system possessing the construction, combination of elements and arrangement of parts which are exemplified in the following detailed disclosure.